1. Field of the Invention
The present invention relates to a zoom lens.
2. Description of the Related Art
As a large-aperture telephoto zoom lens of F2.8 class, a zoom lens shown in Japanese Patent Application Laid-open Publication No. 2007-212830 or Japanese Patent Application Laid-open Publication No. 2010-191336 has hitherto been proposed.
In Japanese Patent Application Laid-open Publication No. 2007-212830, a four-unit zoom lens with a refractive power of lens units in order of a positive refractive power, a negative refractive power, a positive refractive power, and a positive refractive power from an object side has been disclosed. In such type of zoom lens, zooming is carried out by a movement of a second lens unit having a negative refractive power and a third lens unit having a positive refractive power. Moreover, the first lens unit having a positive refractive power is divided into a front-unit and a rear-unit, and focusing is carried out by a movement of the front-unit. According to such an arrangement, the zoom lens is a telephoto zoom lens with an interchangeable lens application of a class of zooming ratio of three times.
In Japanese Patent application Laid-open Publication No. 2010-191336, a five-unit zoom lens with a refractive power of lens units in order of a positive refractive power, a negative refractive power, a positive refractive power, a negative refractive power, and a positive refractive power in order from the object side has been disclosed. In such type of zoom lens, zooming is carried out by movement of the second lens unit having a negative refractive power, the third lens unit having a positive refractive power, and the fourth lens unit having a negative refractive power. Moreover, focusing is carried out by movement of the third lens unit having a positive refractive power. According to such an arrangement, the zoom lens is a telephoto zoom lens with an interchangeable lens application of the class of zooming ratio of three times.
However, in recent years, there has been an increase in a need not only of still photography but also of video photography, and a lens system in which, a video photography function is optimized even in cameras such as an integrated-lens type camera and a digital camera of an interchangeable-lens type, has been sought.
Generally, in video photography, it is necessary to maintain a focused state by moving an auto-focus function all the time. As one of the methods for this, a method of moving a focusing lens unit in the vicinity of a focusing position by a minute amount (called as wobbling) has been known. By carrying out wobbling, a change in a contrast of an image on an image pickup surface is measured, and in a case in which, a judgment is made that the focusing state has changed, the focusing lens is to be moved appropriately once again to refocus. By such wobbling function, even if a distance between the zoom lens and an object changes, the focusing state is maintained continuously all the time, but an extreme high-velocity operation is necessary in accordance with a frame rate of a camera main body. For carrying out an appropriate drive control, the focusing lens unit is sought to be light-weight and with a small amount of movement. Moreover, a reduction in sound which is generated due to wobbling is also sought for reduction in noise at the time of video photography. Although the focusing lens unit and the wobbling lens unit are same normally in most of the cases, sometimes the focusing lens unit and the wobbling unit are arranged as separate lens units.
Moreover, a method of carrying out focusing by detecting a phase difference of an object image on the image pickup surface from a light ray that has passed through different pupil positions, and calculating an object distance, has also been known.